Low impact flow control device

Abstract

A flow control system which is capable of selectively operating at least one pneumatic cylinder between high and low pressures. The flow control system allows the cylinder to engage a workpiece while under the influence of the lower pressure so as to minimize the impact on the workpiece, and thereafter subjects the cylinder to the higher pressure so as to increase the clamping load on the workpiece. Flow control is achieved by controlling the flow of high pressure air from a suitable source with a pilot-operated five ported four-way two-position control valve, a pressure regulator and a unidirectional flow control valve having an adjustable orifice. The pressure regulator is connected to one outlet port of the control valve such that the cylinder is initially supplied with air at the lower pressure when the control valve is in its normal operating position. Once the cylinder engages the workpiece, air pressure to the pilot sufficiently increases to spool the control valve to an actuated position, in which the higher air pressure provided by the supply source is delivered through the control valve to the cylinder. As a result, the clamping load of the cylinder on the workpiece is increased. The flow control system is particularly suitable for operating pneumatic cylinders which are used to actuate the electrodes of a welding gun.

What is claimed is: 
     
       1. A pressure control system for regulating a pressurized fluid between a supply source and a predetermined lower second pressure level, said pressurized fluid being supplied by said supply source to a cylinder that actuates a work performing device into engagement with a workpiece, said pressure control system comprising: regulating means in fluidic communication with said supply source and said cylinder for regulating fluid flow from said supply source to said cylinder, said supply source having a first supply source pressure level, said regulating means being operable between a first position and a second position such that said cylinder is selectively in fluidic communication with said supply source when said regulating means is in both said first and second positions;   first means in fluidic communication with said regulating means and said cylinder for reducing the pressure of said pressurized fluid supplied to said cylinder from said first supply source pressure level to said second predetermined lower pressure level when said regulating means is in said first position, such that said pressurized fluid is delivered to said cylinder at said second predetermined lower pressure level; and   second means in fluidic communication with said regulating means for urging said regulating means from said first position to said second position once said work performing device engages said workpiece, such that said pressurized fluid is delivered to said cylinder at said first supply source pressure level;   whereby said pressurized fluid is at said second predetermined lower pressure level when said regulating means is in said first position so as to stroke said work performing device into low impact engagement with said workpiece, and said pressurized fluid is at said first supply source pressure level when said regulating means is in said second position so as to increase an output load generated by said cylinder on said workpiece, said first supply source pressure level being higher than said second predetermined lower pressure level.   
     
     
       2. The pressure control system of claim 1 wherein said regulating means comprises a control valve having an inlet port in fluidic communication with said supply source, a first outlet port in fluidic communication with said cylinder through said first means, and a second outlet port in fluidic communication with said cylinder. 
     
     
       3. The pressure control system of claim 2 further comprising an exhaust port in said control valve, said exhaust port being in fluidic communication with said second outlet port when said control valve is in said first position, said exhaust port being closed when said control valve is in said second position. 
     
     
       4. The pressure control system of claim 3 further comprising pressure relief means in fluidic communication with said exhaust port. 
     
     
       5. The pressure control system of claim 1 wherein said second means comprises an orifice in fluidic communication with said supply source and said regulating means, said orifice being sized such that fluid flow through said orifice urges said regulating means from said first position to said second position after said work performing device engages said workpiece. 
     
     
       6. The pressure control system of claim 1 wherein said first means comprises a pressure regulator. 
     
     
       7. A pressure control system for regulating a fluid pressure to at least one cylinder which actuates a corresponding pair of electrodes into and out of engagement with a workpiece, said pressure control system comprising: means for supplying a pressurized fluid to said at least one cylinder at a first pressure level;   flow regulating means in fluidic communication with said supply means and said at least one cylinder for regulating flow of said pressurized fluid from said supply means to said at least one cylinder, said supply means having a first supply pressure level, said flow regulating means being operable between a first position and a second position such that said at least one cylinder is selectively in fluidic communication with said supply means when said flow regulating means is in both said first and second positions;   first means in fluidic communication with said flow regulating means and said at least one cylinder for reducing said fluid pressure supplied to said cylinder from said first supply pressure level to a second lower pressure level when said flow regulating means is in said first position, such that said pressurized fluid is delivered to said at least one cylinder at said second lower pressure level; and   second means in fluidic communication with said flow regulating means for urging said flow regulating means from said first position to said second position, such that said pressurized fluid is delivered to said at least one cylinder at said first supply pressure level;   whereby said fluid pressure is at said second lower pressure level when said flow regulating means is in said first position so as to stroke said pair of electrodes into low impact engagement with said workpiece, and said fluid pressure is at said first supply pressure level when said flow regulating means is in said second position so as to increase a clamping load generated by said at least one cylinder on said workpiece.   
     
     
       8. The pressure control system of claim 7 wherein said flow regulating means comprises a control valve having an inlet port in fluidic communication with said supply means, a first outlet port in fluidic communication with said at least one cylinder through said first means, and a second outlet port in fluidic communication with said at least one cylinder. 
     
     
       9. The pressure control system of claim 8 wherein said inlet port is in fluidic communication with said first outlet port when said control valve is in said first position, and wherein said inlet port is in fluidic communication with said second outlet port when said control valve is in said second position. 
     
     
       10. The pressure control system of claim 8 further comprising an exhaust port in said control valve, said exhaust port being in fluidic communication with said second outlet port when said control valve is in said first position, said exhaust port being closed when said control valve is in said second position. 
     
     
       11. The pressure control system of claim 10 further comprising pressure relief means in fluidic communication with said exhaust port. 
     
     
       12. The pressure control system of claim 7 wherein said second means comprises an orifice in fluidic communication with said supply means and said flow regulating means, said orifice being sized such that fluid flow through said orifice urges said flow regulating means from said first position to said second position after said pair of electrodes engage said workpiece. 
     
     
       13. The pressure control system of claim 7 wherein said first means comprises a pressure regulator. 
     
     
       14. The pressure control system of claim 7 wherein said second lower pressure level is no more than about 15 psig. 
     
     
       15. A method for engaging a workpiece with a pair of welding electrodes which are actuated by at least one corresponding cylinder with a fluid at a first pressure level, and then clamping said workpiece with said pair of welding electrodes while said at least one cylinder is under the influence of said fluid at a second pressure level which is higher than said first pressure level, said method comprising the steps of: supplying said fluid at said second pressure level from a fluid source to a flow regulating device;   reducing the pressure of said fluid from said second pressure level to said first pressure level while said fluid flows through a first passage when said flow regulating device is in a first position;   monitoring the flow of said fluid through said flow regulating device and said first passage such that said fluid is delivered to said at least one cylinder through said first passage, whereby said pair of welding electrodes engage said workpiece while said at least one cylinder is stroked under the influence of said fluid at said first pressure level; and   urging said flow regulating device to a second position once said pair of welding electrodes has engaged said workpiece such that said fluid is delivered at said second pressure level to said at least one cylinder through a second passage to enable said at least one cylinder to apply a clamping load to said workpiece;   whereby undesirable impacting of said pair of welding electrodes against said workpiece is substantially avoided by initially engaging said workpiece with said pair of welding electrodes while said at least one cylinder is under the influence of said fluid at said first pressure level so as to initially engage said workpiece with a force which is less than said clamping load.   
     
     
       16. The method of claim 15 wherein the step of urging said flow regulating device to said second position comprises supplying said fluid at said second pressure level through an orifice to said flow regulating device, such that fluid pressure downstream of said orifice sufficiently increases so as to urge said flow regulating device from said first position to said second position. 
     
     
       17. The method of claim 16 wherein the rate at which said fluid is supplied to said flow regulating device through said orifice increases once said pair of welding electrodes engages said workpiece. 
     
     
       18. The method of claim 15 further comprising the steps of venting said fluid from said at least one cylinder through said flow regulating device by venting said fluid at said fluid source. 
     
     
       19. The method of claim 18 wherein said step of venting causes said flow regulating device to return to said first position, such that said fluid is vented through an exhaust port in said flow regulating device. 
     
     
       20. The method of claim 15 wherein said step of reducing the pressure of said fluid includes regulating said first pressure level to a pressure of no more than about 15 psig.